This invention relates generally to injection molding and more particularly to mechanism for actuating injection molding valve pins.
In order to control the flow of pressurized melt through the runner from the molding machine into the cavities, it is necessary that the movement of the valve pin tips into the gates be precisely controlled. Considerable force must be applied to the valve pins to actuate them to closed sealing positions in the gates and when this force is removed, the melt pressure returns the valve pins to the open position.
In the past, valve pins have been actuated by a variety of mechanical mechanisms, one of which utilizes a lever and air cylinder arrangement for each valve pin. These have been found to be subject to malfunction, particularly in high speed applications where the melt pressure may be above 20,000 psi. When opening, the high melt pressure drives the valve pins against the mechanism with considerable impact, causing it to have a reduced operating life. In larger volume applications involving a considerable number of valve pins, the requirement of separate mechanism for each valve pin also has the disadvantage of being very costly to install and maintain.